1. Field of the Invention
The present invention relates to photoelectron systems. More particularly, to a vertical silicon photomultiplier with superior quantum efficiency at optical wavelengths.
2. Description of the Related Art
In recent years, silicon photomultipliers (SiPMs) have developed to replace photomultipliers (PMTs). Silicon photomultipliers (SiPMs) are advantageous in that they are relatively small in size, low in operation voltage, for example, 25˜100 V, and not affected by electric fields, compared with photomultipliers (PMTs). On the contrary, silicon photomultipliers (SiPMs) have a disadvantage in that their quantum efficiency is very low, less than 10%, with respect to ultraviolet light of wavelengths 200˜400 nm. To resolve this problem, SiPM research is focused on maximizing the quantum efficiency in light of wavelengths 200˜900 nm.
FIG. 1 is a cross-sectional view illustrating a general silicon photomultiplier. As shown in FIG. 1, the general silicon photomultiplier 100 is configured to include a substrate, an epitaxial layer 130 formed less than 5 μm thick on the substrate, and a PN-junction layer 120 formed in the epitaxial layer 130 by sequentially injecting P+ ions and N+ ions. In the epitaxial layer 130, relatively strong electric fields are generated. Incident light (photon) generates electron-hole pairs in the epitaxial layer 130. The electron-hole pairs are accelerated by strong electric fields in the epitaxial layer 130 and cause an avalanche breakdown, which amplifies an input signal. However, since the PN-junction layer 120 is formed parallel to the substrate 140 but electric fields are vertically generated perpendicular to the substrate 140, ultraviolet light 30 may have difficulty reaching the PN-junction layer 120 in the epitaxial layer 130. Therefore, the general silicon photomultiplier has low quantum efficiency. In addition, since the epitaxial layer 130 reacting to incident light is approximately 5 μm thick, the infrared light 20 is transmitted to a relatively deep depth of the silicon photomultiplier and does not have an opportunity to be activated with the layer. Therefore, the general silicon photomultiplier has low quantum efficiency.